An example of a locking device of this type is art taught by WO2006/132018. In this art, a locking mechanism is provided to a seat side and a striker is provided to a vehicle body side. The locking mechanism includes a base plate having a recess capable of receiving the striker, a hook, a pawl, a release lever and a thrust member.
The hook is rotatably supported on the base plate, so as to form a locked condition in which the striker is held between the hook and the recess of the base plate or an unlocked condition in which the hook is spaced from the striker. The pawl, the release lever and the thrust member are respectively coaxially rotatably supported on the base plate. The pawl rotates to a condition in which the pawl engages the hook, so as to maintain the hook in the locked condition. The release lever, when applied with a manipulation force for unlocking, rotates the pawl from an engaging position in which the pawl engages the hook in a non-engaging direction. The thrust member further presses the hook placed in the locked condition in a locking direction. Further, the thrust member rotates with the rotation of the pawl in the non-engaging direction.
A locking spring is positioned between the hook and the pawl. The locking spring biases the hook and the pawl such that the hook and the pawl are stabilized at a rotational position corresponding to the locked condition or the unlocked condition. Also, a thrust spring is positioned between the cam and the base plate. The thrust spring biases the thrust member to press the hook in the locking direction, thereby reducing a clearance between the locking mechanism and the striker in the locked condition.
In the art taught by Patent Document 1, both of the release lever and the thrust member are coaxially rotatably supported on the base plate. Therefore, if a rotational angle of the thrust member pressing the hook placed in the locked condition in the locking direction is increased, a rotational angle of the release lever can be increased at the time of unlocking. This may lead to an increased manipulation load. Conversely, if the rotational angle of the release lever is determined so as to fall in a desired angle range, a range (in which the thrust member can press the hook placed in the locked condition) can be reduced. As a result, clearance-absorbing performance to reduce the clearance between the locking mechanism and the striker may be reduced. Therefore, depending on dimension errors of the locking mechanism and the striker or deformation thereof with long-term use, the clearance cannot be reliably reduced.
Further, when the clearance-absorbing performance to reduce the clearance is limited, it is difficult to apply a resin coating to the recess of the base plate and the hook in order to prevent noise generation caused by metal-to-metal contact at the time of locking. The resin coating may have excellent impact noise absorption performance. However, the resin coating may be easily subjected to plastic deformation and wear. Therefore, the clearance between the locking mechanism and the striker can be easily increased, so that the clearance cannot be reliably reduced.
Thus, there is a need in the art to provide increased clearance-absorbing performance to reduce a clearance between a locking mechanism and a striker in a locked condition without increasing a manipulation range of a release lever, so that the clearance can constantly be reliably reduced.